Balanced parentheses? in #PHP

troll.php

<?php

function isBalanced($str){
    $count = 0;
    $length = strlen($str);
    for($i = 0; $i < $length; $i++){
        if($str[$i] == '(')
            $count += 1;
        else if($str[$i] == ')')
            $count -= 1;
        if($count == -1)
            return false;
    }
    return $count == 0;
}

$list = array("", "(", ")", "()", "(())", "(()", "())", "())(", "(())", "x", "(x", "()x", "x)", "x(y(z))", "x(y)z)(");
foreach($list as $str){
    echo $str . " : " . (isBalanced($str) ? "ok" : "ko") . "\n";
}